cfg80211: make BSSID generation function inline

This will enable reuse by mac80211.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Change-Id: Ia226daa73f1aa0c99332bdff035cc5a570b70cfa
CRs-fixed: 2399972
Git-commit: 7ece9c372b21635120e7ab5ea3fc41ce9892ead8
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next.git


Signed-off-by: Peng Xu <pxu@codeaurora.org>